1. Field of the Invention
This invention relates to a driving torque controlling system for a vehicle wherein driving torque of an engine is reduced rapidly in response to a magnitude of lateral acceleration which may be produced upon turning of the vehicle or to an amount of slip of a driving wheel upon acceleration of the vehicle in order to assure safe running of the vehicle.
2. Description of Background Art
When the condition of a road on which a vehicle is driving varies suddenly or when a vehicle is driving on a slippery road having a low coefficient of friction such as, for example, a snowy road or a frozen road, it frequently occurs that a driving wheel of the vehicle rotates slipping or in vain.
In such an instance, it is very difficult even for a skilled driver to adjust the amount of operation of an accelerator pedal to control the output power of an engine skillfully so that the driving wheel may not rotate slipping or in vain.
Similarly, a vehicle which is driving on a curved road is acted upon by centrifugal force corresponding to lateral acceleration of a direction perpendicular to the driving direction. Accordingly, when the driving speed of the vehicle on the curved road is excessively high, it may exceed a limit of gripping force of a tire to cause lateral slipping of the body of the vehicle.
In such an instance, in order to reduce the output power of the engine appropriately so that the vehicle can drive with safety with a turning radius corresponding to the curved road, particularly when no exit of the curved road can be found out or where the radius of curvature of the curved road decreases gradually, a very high driving technique is required.
With conventional vehicles having a so-called under-steering tendency, it is necessary to gradually increase the steering amount in accordance with an increase of lateral acceleration acting upon the vehicle. However, if such lateral acceleration exceeds a particular value peculiar to the vehicle, then the steering amount increases suddenly, which makes desired turning driving difficult. It is well known that such tendency is prominent particularly with vehicles of the front engine front drive type which have a strong understeering tendency.
From such circumstances, several improved driving torque controlling systems have been proposed, and in an exemplary one of such systems, a slipping condition of a driving wheel is detected and, if a slip of the driving wheel takes place, the output power of the engine is reduced compulsorily independently of an amount of operation of the accelerator pedal by the driver. In another exemplary one of the improved driving torque controlling systems, lateral acceleration of the vehicle is detected and, before a turning limit across which it is difficult for the vehicle to turn is reached, the output power of the engine is reduced compulsorily independently of an amount of operation of the accelerator pedal by the driver. Due to such driving torque controlling systems, the driver can select, when it is considered necessary, one of driving of the vehicle in which the driving torque controlling system is used and normal driving in which the output power of the engine is controlled in response to an amount of operation of the accelerator pedal.
In one of such vehicle driving torque controlling systems, a rotational speed of a driving wheel and another rotational speed of a driven wheel are detected and, considering a difference between the rotational speeds as an amount of slip of the driving wheel, the driving torque of the engine is controlled in response to such slip amount. Another vehicle driving torque controlling system controls the driving torque of the engine in response to an amount of yawing (hereinafter referred to as yaw rate) or the like of the vehicle.
In the case of the latter means, since yawing and so forth of the vehicle which are produced mainly during high speed quick turning of the vehicle have a tendency that the amounts thereof increase suddenly as the speed of the vehicle increases and the turning motion of the vehicle becomes quick, a yaw rate is detected by means of a vibration sensor, an acceleration sensor or the like, and the driving torque of the engine is reduced when the yaw rate exceeds a predetermined level.
Where such driving torque controlling system is employed, it is also possible to reduce a shock and so forth during a gear shifting operation of an automatic transmission.
When the driving safety of a vehicle is considered, it is desirable for the vehicle to include thereon a driving torque controlling system which detects a slipping condition of a driving wheel and compulsorily reduces, when a slipping condition of the driving wheel takes place, the output power of the engine independently of an amount of operation of the accelerator pedal by a driver and another controlling system which detects lateral acceleration of the vehicle and compulsorily reduces, before it becomes difficult or impossible for the vehicle to turn, the output power of the engine independently of an amount of operation of the accelerator pedal by the driver.
However, no conventional vehicles include both of an output controlling system which compulsorily reduces, when a slipping condition of a driving wheel takes place, the output power of the engine independently of an amount of operation of the accelerator pedal by the driver and another output controlling system which compulsorily reduces, before it becomes difficult or impossible for the vehicle to turn, the output power of the engine independently of an amount of operation of the accelerator pedal by the driver. Accordingly, in case a slip of a driving wheel takes place and simultaneously the vehicle is likely to become difficult to turn, it is a problem how much the driving torque of the engine should be reduced in order to permit the vehicle to keep its posture properly and drive with safety and certainty without failing to satisfy the intention of the driver much.